Small volume arc discharge lamps are being developed for use as vehicle headlamps. These lamps offer long service lives and have high electrical efficiency. In addition, such lamps have small optical sources and thus are well adapted to headlamp optics. The enclosed volume of such lamps is roughly that of a pea, so the lamp may be fabricated from a small diameter quartz tube. Since the light source itself is small, the reflector optics may be made correspondingly small.
In order to obtain the required light output pattern, the arc tube must be precisely located within a reflector. The requirement for precise positioning of the arc tube in the reflector and for focusing the lamp assembly may cause difficulties in manufacturing. Additionally, when ignited, the arc tube becomes hot, thereby requiring that support materials for the arc tube be able to withstand high temperature operation. Although metals and ceramics have been used to support arc tubes in the past because of their ability to withstand high temperatures, these materials are hard. Thus, precise mounting of the arc tube using a metal or ceramic support structure can cause stress in the arc tube. Since the conventional manufacture of arc tubes and support structures normally results in some dimensional variation, some manufactured arc tubes will have high pressure contact and high stress, whereas others will have low contact pressure and low stress. Coupling stress is made worst by thermal expansion and contraction of the components as the arc tube is turned on and off. Finally, the arc tube can be caused to fracture if a portion of it is pinched in a support structure. Thus, the need exists for an arc discharge headlamp assembly that can withstand the temperatures of operation and still allow the arc discharge tube to be precisely positioned and focused without applying excessive stress to the tube.
A related problem concerns the energy management of the arc tube. The physics of the arc process is carefully designed for a particular operating temperature. Where thermal conduction from an arc tube differs from the design value, for example, when the support structure has a relatively low or relatively high amount of contact with the arc tube, heat builds up or is lost too quickly from the arc tube. In this situation, the physics of the arc changes, thereby affecting the lamp optics and color. There is a need for a support structure that forms a consistent thermal contact from one arc tube to the next.
U.S. Pat. No. 4,734,612 issued Mar. 29, 1988 to Sasaki et al discloses a double ended lamp capsule with leads welded to support wires. One support wire extends through an insulating sleeve and then in parallel with a second wire extends through a seal area of an enclosing capsule.
U.S. Pat. No. 4,754,373 issued Jun., 28, 1988 to Otto et al discloses a double ended filament lamp capsule positioned in an automotive headlamp reflector. The reference discloses a structure in which a double ended lamp capsule may be welded and axially aligned as part of a headlamp.
U.S. Pat. No. 5,032,758 issued Jul. 16, 1991 to Davenport et al discloses an arc discharge lamp axially aligned in a reflector.
U.S. Pat. No. 5,036,439 issued Jul. 30, 1991 to Hoffmann et al discloses a double ended arc discharge lamp held in a metal reflector or shield. The reflector includes spring tabs that press against the lamp tube to properly position the shield.
U.S. Pat. No. 5,039,904 issued Aug. 13, 1991 to Kosmatka et al discloses a double ended arc discharge tube axially mounted in a headlamp. One end of the tube is secured in a threaded structure including 0-rings. The forward lead extends away from the lamp capsule and passes through the reflector body for exterior electrical connection.
U.S. Pat. No. 5,051,658 issued Sep. 24, 1991 to VanPijkeren discloses a double ended arc discharge tube wherein one end is pinched between two metal arms. The arms are supported on a bushing that is in turn connected to a tube and holder body.
U.S. Pat. No. 5,059,855 issued Oct. 22, 1991 to Irisawa et al discloses a double ended arc discharge tube welded by its leads at each end. The forward lead extends back through an insulating sleeve to a base. The leads are ducted through the body of the base.
U.S. Pat. No. 5,130,911 issued Jul. 14, 1992 to Eisner, Sr. discloses a two-piece lamp retainer for holding a press sealed tungsten halogen capsule in a headlamp.
U.S. Pat. No. 5,291,092 issued Mar. 1, 1994 to Coushaine discloses a double ended arc discharge headlamp assembly including an arc tube, wedge, retainer, forward connector rod, insulating sleeve, RF ring and base. The wedge secures one end of the arc tube and is compressed along its exterior by the retainer. The lamp, wedge and retainer are movable relative to the base to permit alignment. Following alignment, the RF ring is fused to the base and to the retainer.
Pending application Ser. No. 08/354,508 filed Dec. 13, 1994 discloses a double ended arc discharge headlamp assembly wherein a split ball assembly is mounted about one end of an arc discharge tube. The split ball assembly is held in place by concave portions in the base and by a locking nut.